This disclosure relates generally to a cathode for use in an x-ray tube assembly and more particularly to a method for electro-discharge machining a cathode for use in an x-ray tube assembly.
Existing medical x-ray tube assemblies include a cathode assembly having an emitter and a cup. The cathode assembly is orientated to face an x-ray tube anode, or target, which is typically a planar metal or composite structure. The space between the cathode and the anode is evacuated.
A concern with existing cathode designs is that the emitter, often a helically coiled tungsten wire filament, tends to be large and electrons are emitted radially outward from all side surfaces of the filament surface. The filaments are therefore positioned within a cup that is designed to produce a tailored electric potential distribution in the vacuum such that all electron trajectories are redirected from the initial divergent motion toward a focal spot on the anode surface. This is accomplished by way of carefully machining the cathode cup to passively shape the electric field leading to the focal spot. This often takes the form of multiple transverse slots formed in the center of the cathode cup.
The use of common machining techniques, however, tends to result in a large transverse section removed from the cup. This leaves sections of the cup with sharp features at the edges of the cup referred to as ears. These sharp features lead to high electric field stress and undesirable consequences of high voltage stability issues. In order to compensate for such sharp-eared features, one approach has been to install a ring shield around the perimeter of the cup. This approach, however, introduces an increase in cost due to additional part manufacturing and an increase in complexity of the cathode assembly. A cathode cup assembly with improved design and manufacturing that eliminated the need for a separate ring shield while providing improved high voltage stability would provide for improved tailored performance of the x-ray assembly and may be used to reduce manufacturing and assembly costs.
Therefore, it would be desirable to provide a method for manufacturing a cathode assembly that has smooth cathode cup surfaces suitable for high voltage stability. Additionally, it would be highly desirable to provide a method for producing a cathode assembly that has adequate shielding without requiring additional part manufacturing and assembly.